Every time something like this happens, the social contract is undermined, and policing by consent is made harder.
Police feeling embattled, misunderstood, and increasingly under scrutiny and under siege, seeking to defend, and explain away such actions, does nothing to help mitigate such erosion.
For myself, at first glance, I cannot see how this can be justified as reasonable force.
However, I'm prepared to accept an independent inquiry that receives all evidence and witness statements, and that independent inquiry's outcomes.
Police are not intended to decide guilt, and carry out sentencing. They are there to uphold the law, and detain and present alleged wrongdoers for determination of guilt and sentencing.
They certainly are not there to vent their spleen with their boots on an available target's head.